Microsoft released the first developer preview of Windows 8, which contains the most sweeping changes to user interface design the operating system has ever seen. The beta OS, unveiled at the Microsoft Professional Developers' Conference in Anaheim last week, offers two different user interface modes, one that looks like Windows 7 and another that looks and acts like a mobile device user interface -- even more so than Apple's Lion.

Microsoft demo'd Windows 8 on a Samsung tablet with an Intel Core i5 processor, and said that it will eventually support ARM-powered tablets. The developer preview also runs on the same PC hardware as Windows 7 and Vista. You can also virtualize it with the latest software from VMware. On a Mac, that's VMware Fusion 4. On a PC, it runs in a VMware Workstation 8 virtual machine. I downloaded it over the weekend take a look at it running in the new VMware Fusion 4.

Windows 8 Metro mode looks nothing like Windows--or any other OS

Windows 8 Metro doesn't do windows

Once you install Windows 8 and log-in, you get to something that looks nothing like Windows, or any other PC operating system. This is the new tablet-like Metro mode. The Metro home screen consists of sets of large tiles that launch apps when you click them. Some tiles also display changing bits of information, such as stock quotes or news headlines. The home screen is labeled Start but fills the screen and extends beyond it. The app tiles scroll left and right, like the icons on an iPhone/iPad home screen. You can rearrange the tiles by dragging them. Right-click a tile, and a toolbar that appears at the bottom with options to uninstall the app or to make the tile larger or smaller. A Control Panel tile offers settings for Metro mode.

Windows 8 Metro has no windows. When you launch an app, it fills the screen. There is no menu bar, as in Windows. Some of the demo apps have navigation similar to Windows Phone 7. A right-click brings up bars at the top and bottom of the screen.

Clicking on a tile called Desktop takes you into the standard Windows mode, which looks and acts a lot like Windows 7 in this build. Windows Explorer has been updated with a new Office-like ribbon for accessing frequently used tasks. A more drastic difference between the Windows mode and Windows 7 is that clicking on the Start button takes you back into Metro. To get to some of the features of the old Start menu, hover the mouse over the far left bottom corner without clicking, and a small menu pops up. If you chose Search, a new bar slides out on the right side containing a Search field and icons for searching in specific areas. This same bar can appear in Metro mode, and is brought up the same way.

To log off from Metro mode, click the user icon in the upper right to bring up a menu. The text here is fairly large, as are the tiles. The screen shots show a small 800x600 resolution (again, this was in VMware Fusion), but even taking that into consideration, the user interface elements are significantly larger than those in Windows 7 or Mac OS X.

Searching in the Windows mode , with the new Windows Explorer behind

Windows 8 and Lion

Like Apple, Microsoft sees the future as a melding of PC and handheld device OS's. Metro goes farther than Lion does. Lion is basically Mac OS X with some iOS do-dads: full-screen mode, Launch Pad to mimic the iOS home screen, scroll bars that disappear, and touch pad gestures that are more like iOS than Snow Leopard.

Windows 8 isn't as much as a melding of two OS's as it is two OS's stuck together in one box. The Metro and Windows 7-like modes each have a completely different APIs, which means developers will have to create two versions of an app if they want it to run in both modes. For instance, there are two different aspects of Internet Explorer, one launched from Metro, and one launched for the standard Windows mode. Like Safari on iOS, the Metro version of IE doesn't support Flash. It supports HTML5. The IE in standard Windows mode, however, does support Flash and the usual plug-ins.

Metro feels like a tablet OS (and a potentially good one), not just a PC OS with tablet user interface features. But when running on a PC (or Mac in virtualization), Metro doesn't appear at this point to have any advantage over the standard Windows mode. I admint that this is subjective territory. I also don't find the iOS-like features of Lion all that compelling: I never touch Launch Pad or full-screen mode, I've turned on the display of scrollbars and set gestures back to the way Leopard and Snow Leopard handle them. (And I miss double-tap to drag.) But Windows 8 Metro is so different that these kinds of critiques don't apply.

Interface elements in Windows 8 Metro are large and tablet-like--nothing like Lion's iOS-like features

The low down

This first developer preview is clearly an early build, and is not partcularly stable. I got to experience the new, friendlier Blue Screen of Death, which sports a plain-English error message ("Your PC ran into a problem it couldn't handle").

It's too early to pass judgment on stability or on the merits of the dual-personality user interface of Windows 8. In the year or so between this developer preview and the final product, both Metro and Windows modes are likely to gain major enhancements, new features, and refinements that we haven't seen yet. Microsoft said that business applications such as Office will have additional UI features such as ribbon bars, menus, and floating palettes.

One benefit to Metro would be the ability to run tablet apps on a PC -- something Apple's OS's can't do. Even more compelling would be the ability to run Windows-like applications--such as Office--in Metro. ARM tablets would not be able to Windows 7 applications, but new apps written for both modes of Windows 8 could.

It is clear, however, that the Metro interface only makes sense if Microsoft becomes a major player in the tablet market. Whether this happens or not is the $64,000 question. Windows Phone 7 hasn't succeeded, and last April, CNN Money quoted Neil MacDonald, a Gartner analyst saying that Microsoft is "two generations behind Apple and Google" in developing a tablet OS. But writing off Windows 8 in the tablet market is as baseless as the analyst who predicted last week that Windows 8 tablets will have 15 percent market share by 2014. I do feel safe in predicting that Windows 8 will be the most innovative thing to come out of Microsoft since Windows 95.